From Beacon to Amber, Flywheels Missed the Grid

Flywheel energy storage systems, once hailed for their mechanical elegance and rapid response capabilities, have struggled to establish a significant foothold in the grid storage market despite decades of development and government support. These systems store energy by spinning a mass and converting kinetic energy back into electricity, offering advantages such as fast reaction times, durability, and avoidance of chemical degradation typical of batteries. However, by 2026, flywheels remain a niche technology, with many questioning their viability as a mainstream solution for large-scale energy storage. The history of flywheel development reveals sustained interest and investment, particularly from the US Department of Energy (DOE), which supported research and commercialisation efforts from the 1970s through the early 2010s. Notable projects included Beacon Power’s Stephentown and Hazle Spindle plants, which operated as frequency regulation facilities rather than bulk energy storage sites. Despite receiving tens of millions in funding, these projects demonstrated that while flywheels excelled at rapid power injection and absorption, their high cost per kilowatt-hour and limited energy capacity restricted their commercial success. Beacon Power’s eventual bankruptcy and asset sales underscored the challenge of converting technical promise into a viable business model. Amber Kinetics represents a more recent attempt to expand flywheel applications into longer-duration storage, with its M32 unit offering four hours of discharge at 32 kWh capacity. While this marks a technical advancement, the scale remains a significant barrier. Compared to modern lithium-ion battery containers that store several megawatt-hours, Amber’s units are comparatively small, requiring thousands of modules to match the energy capacity of a single battery installation. This modular limitation, combined with the complexity and cost of integrating many units, raises questions about the commercial practicality of flywheels competing with rapidly advancing battery technologies. The DOE’s current long-duration storage strategy reflects this reality, focusing on technologies like compressed air and pumped hydro rather than flywheels. Although the department cautions against interpreting this as a formal ranking, the absence of flywheels from prominent future storage portfolios signals a shift in priorities. The market’s preference for scalable, cost-effective solutions continues to favour lithium-ion batteries and other emerging technologies, leaving flywheels as a specialised tool rather than a broad solution for grid-scale energy storage. Ultimately, flywheels have proven their technical capabilities but have struggled to find a sustainable commercial niche beyond fast frequency regulation services. As energy markets evolve and storage demands grow, the challenge for flywheel developers lies in overcoming scale and cost hurdles to compete with more established battery systems. Without significant breakthroughs or new market incentives, flywheels may remain a peripheral technology in the broader landscape of grid energy storage.